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EARLY EVALUATION OF PULMONARY FUNCTIONS OF PATIENTS WITH MINIMALLY INVASIVE DIRECT CORONARY ARTERY BYPASS GRAFT SURGERY

An Overview:

Despite the technical improvement in the management of cardiac surgery, pulmonary function following cardiac surgery is still a challenge for cardiac surgeons. This topic was and still is being studied. This is an attempt to address this fascinating, and vital issue, within the constraints prevailing here.

In our country, patients with coronary artery disease are referred to this institute. A significant number of patients are managed in NICVD. A total of 750 patients were operated in NICVD in the year 2007, out of which 265 were CABG, 60 of which were MIDCAB procedure and remaining were conventional on-pump procedure CABG. So far only one study was done to evaluate pulmonary function after on-pump CABG. No comparative study was done on pulmonary outcomes between MIDCAB and conventional on-pump CABG procedure. In this study, we have tried to evaluate pulmonary outcomes after CABG surgery and to compare the incidence between MIDCAB and conventional on-pump CABG procedure.

Recently, a variety of Novel approaches and ingenious techniques have been developed in an attempt to make cardiac surgical procedures less invasive. Many of these methods remains largely experimental, Yet one procedure seems to have been rapidly accepted by Cardiac surgeon. MIDCAB Stands for a less invasive procedure because here three component of invasive nature like (a) Cardio pulmonary bypass. (b) Sternotomy and (c) aortic manipulation are obviated (Izzat and Yim, 1997).

MIDCAB was developed as a less invasive approach toward bypass surgery. Because a smaller incision is used, patients recover more quickly, with less trauma and short time as compared to conventional CABG. Recovery time after MIDCAB is comparable to recovery time after balloon angioplasty (3 to 7 days) versus the two weeks that are common after conventional CABG. Within two weeks, many MIDCAB patients can return to normal activities (Elhendy et al., 2007).

Regardless of the recent advances in technology with cardiopulmonary bypass (CPB), postoperative pulmonary dysfunction continues to be an important cause of morbidity. Although severe postoperative acute

respiratory distress syndrome is now rare, significant impairment of pulmonary function does occur leading to derangement of gas exchange and prolong extubation time (Montes et al., 2004).Pulmonary impairment after cardiac surgery is believed to be multifactorial. Some of the factors contributing to the development of lung dysfunction include atelectasis, increased shunt, and alteration in lung and chest wall mechanics. Surgical factors secondary to sternotomy, pleurotomy and harvesting of internal mammary artery have been implicated. Additionally, it is well accepted that CPB induces an inflammatory response, producing increased pulmonary endothelial permeability and parenchymal damage (Montes et al., 2004).In MIDCAB, coronary revascularization procedure is done without sternotomy incision and CPB, for this impairment of pulmonary function is less marked than conventional CABG because sterna stability is less interfered so compliance remains good (Berrizbeitia et al., 1989).Studies are undergoing throughout the world and it would be prudent for us to compare the postoperative lung function after these procedures for the better understanding of the patients outcome undergoing MIDCAB.

HYPOTHESIS

Pulmonary function is better preserved in minimally invasive direct coronary artery bypass (MIDCAB) patient than Conventional CABG patient.

OBJECTIVES1. To evaluate the lung function after MIDCAB and CCABG surgery.2. To compare arterial blood gases and pulmonary function tests pre and

postoperatively between on-pump CABG and MIDCAB surgery patients.

REVIEW OF LITERATURE

The first report of a left thoracotomy for the implantation of LIMA to LAD as method of treatment for angina pectoris by Kolessov in 1967. In 1995, Benetti & associates reports of minimally invasive coronary operations via a small thoracotomy and without cardiopulmonary bypass opened a new era in the treatment of isolated disease of the LAD (Benetii et al., 1995).

Gu (1998) compared inflammatory responses in 31 MIDCAB and 31 CCABG patients. The patients were randomly assigned in to the two groups. Patient characteristics were similar between the two groups. Length of follow-up was for the preoperative period only and there were no losses to follow-up. However, the inflammatory response markers were

only measured in a subgroup of 20 (32%) patients (10 each for MIDCAB and CCABG). These patients were stated to have no signs of severe heart failure or other organ dysfunction and no history of a bleeding diathesis, and so were likely to represent a healthier cohort than the rest of the patients. There was greater blood loss (p<0.001) for CCABG compared to MIDCAB, more CCABG patients than MIDCAB patients required transfusion in their study (Gu et al.,1998).

In a randomized controlled trial Gulielmos (2000) compared four different surgical techniques for single vessel coronary artery bypass – CCABG with median sternotomy, off-pump with median sternotomy (OPCAB), on-pump minithoracotomy (Dresden technique) and off-pump minithoracotomy (MIDCAB). Most of the main results (pain and post-traumatic stress disorder outcomes) were presented only by the two types of surgical access (i.e. on-pump and off-pump sternotomy versus on-pump and off-pump mini thoracotomy). Where data could be used, the MIDCAB arm (n=9) was compared to the CCABG arm (n=10) and the Dresden CABG arm (n=8). No perioperative death was observed (Gulielmos et al., 2000).

Gulielmos (2000) described the same four arms as above, although there were four additional patients (11%) in this trial (one more each in the OPCAB and MIDCAB arms and two more in the mini thoracotomy arms). Again the data for the main outcomes (inflammatory response) were presented only by the two types of surgical access (i.e. on-pump and off-pump sternotomy versus on-pump and off-pump mini thoracotomy) and so could not be used for this review. Where data could be used, the MIDCAB arm (n=10) was compared to the CCABG arm (n=10) plus the Dresden CABG arm (n=10). No details of the method of concealing allocation to either the MIDCAB or CABG groups was given; the study report stated that ‘One of the four techniques was prospectively chosen for each patient at random’ (Gulielmos et al., 2000).

POEM (Patency, Outcomes and Economics of MIDCAB) (2001) compared 165 MIDCAB patients with 145 CCABG patients. The trial was originally designed to have 200 patients in each arm, but results were only available for a total of 310 patients (Mack et al., 1999). Only 56% of patients returned for angiographic follow-up at six months (62% of MIDCAB patients and 48% of CCABG patients). The POEM investigators intend to follow-up patients for one year and will also compare quality of life between MIDCAB and CCABG patients. At six months follow-up in the POEM trial, there was no discernible difference in mortality was found between the MIDCAB group (four deaths - 2.4%) and the CCABG group (two deaths - 1.5%). The relative risk for postoperative mortality at six months for MIDCAB compared to CCABG was 1.76 (95% confidence

interval (CI) 0.33–9.46). There was no discernible difference between MIDCAB and CCABG in the POEM trial for perioperative or postoperative MI (six month follow-up). The relative risk for perioperative MI with MIDCAB compared to CCABG was 0.22 (95% CI 0.05–1.02). The relative risk for postoperative MI was 2.64 (95% CI 0.11–64.27).

Connolly (2000) was a retrospective review of MIDCAB (125 patients) and CCABG redo (348 patients). The MIDCAB patients were operated on more recently than the CCABG group and also had a higher risk profile. The mean number of grafts was 1.29 (0.7) for the MIDCAB group and 2.9 (1.1) for the CCABG group, (p<0.001). There were a number of arithmetical discrepancies. They showed significantly fewer deaths in MIDCAB patients compared to CCABG patients. Significantly less renal failure with MIDCAB compared to CCABG was observed in their study (Conolly et al., 2000)

Conventional CABG has been around for the past four decades and in that time it has nearly been perfected. Although more than one million of these procedures take place annually with a 99% success rate, this is still a very traumatic and painful surgery for the patient (Elhendy et al., 2007).

Lichtenberg Artur (2000) compared pulmonary function in 15 men who underwent MIDCAB (Group A) and 15 men who underwent CCABG using CPB. Inclusion criteria for both groups were male sex, normal cardiac function (EF >55%), NYHA classification 1 or 11 and absence of pulmonary or chest wall diseases. Pulmonary function was comparable between the two groups on postoperative day 1. Vital capacity was significantly greater in MIDCAB patients than CCABG patients. Similar results were found for FEV1. But postoperative pain was significantly higher in MIDCAB group in POD 1 and POD 3 (Lichtenberg et al.,2000)

Ohkado (2002) compared pulmonary function in 8 patients undergoing MIDCAB, 10 Patient undergoing off-pump coronary artery bypass and 12 patients undergoing CCABG. Parameters were adjusted by their predicted values and postoperative values were expressed as a ratio to preoperative ones. Only MIDCAB group maintained postoperative vital capacity and FEVI close to the preoperative level and thus showed significantly better recovery than other Groups (Ohkado et al.,2002).

Lower Limits of Reference RangesIn pulmonary function testing, three sets of limits are commonly used. The most common defines the normal range for FEV1/FVC as >70% or >75% and the normal range for everything else as the predicted value ± 20% (Crapo, 1998).

Role of Spirometry in Pulmonary Function TestingSpirometry is the most common and useful lung function tests. Its clinical utility has been proved extensively, it is the least expensive test to perform, and it should be the test most widely available in doctor's offices, clinics, and hospitals. The Forced Vital Capacity (FVC) test is performed by having a patient inhale to Total Lung Capacity (TLC) and then makes a maximally forced exhalation into a spirometer. Classically, exhaled volume is measured as a function of time. Flow may also be measured and displayed as a function of exhaled volume. The three primary spirometric indices in the forced test are FVC, forced expiratory volume in 1st second (FEV1), and their ratio, FEV1/FVC. Numerous other spirometric measures are available, but their clinical utility is less well established (Fraser et al., 1999).

Coronary artery bypass surgery and pulmonary functionsMedian sternotomy incision is the standard approach for coronary artery bypass grafting. Usually the bypass conduit consists of a RSVG or the IMA. It is assumed that little or no significant lung injury is sustained during sternotomy that post-sternotomy changes in pulmonary function are related to changes the mechanics of the thoracic cavity itself. However, the combination of sternotomy and IMA harvesting may impair respiratory function. First, it may interfere with sterna stability and decrease chest wall compliance. Second, because of a reduced blood supply to the intercostals muscles, it may decrease the forces of respiration with a corresponding decrease in pulmonary mechanics (Berrizbeitia et al., 1989).

For many years, it has been recognized that patients undergoing cardiac surgery develop variable degrees of respiratory insufficiency postoperatively. In these patients, higher concentrations of oxygen are required to achieve adequate oxygen tension, primarily as a consequence of intrapulmonary shunting regions of atelectasis and alveolar collapse may occur, resulting in airspaces receiving pulmonary blood flow that are not being ventilated, contributing factors may occur. Impaired capillary endothelial integrity may be followed by an increase in interstitial fluid and alveolar edema (Berrizbeitia et al., 1989). Anesthetic agents may effects pulmonary vasoconstriction. Other causes of gas exchange abnormalities after cardiac surgery include central effects from anesthesia and narcotics as well as CNS embolization of air or blood clots. Impairment of carbon dioxide elimination may develop from a rise in alveolar dead space secondary to decreased ventilatory drive from the effects of general anesthesia and/or narcotics. Inadequate tidal volume from neuromuscular weakness may occur. Changes in the mechanics of breathing may occur postoperatively as a result of inhalation anesthetics and / or muscle-paralyzing agents (Stenseth et al., 1996). Pain from the chest incision and thoracic or mediastinal chest tubes may result in

diminished excursion of the chest and diaphragm. Obesity and rare phrenic nerve injury may also play a role (Mathy & Chatterjee, 1997). Postoperatively, early extubation is desirable, appears safe, and does not increase postoperative cardiac or pulmonary morbidity (Michel et al., 1979) in on-pump CABG patients. However, longer periods of mechanical ventilatory support postoperatively may be necessary in patients who develop acute adult respiratory distress syndrome or who have evidence of severe insufficiency postoperatively (Klineberg et al., 1977).

MATERIALS & METHODSStudy design:Prospective non randomized clinical trialPlace of study:The study is carried out in the Department of Cardiac Surgery, National Institute of Cardiovascular Disease, Sher-E-Bangla Nagar, Dhaka, Bangladesh.Study period:July 2006 to June 2008.

Study Population:Patients admitted in the Department of Cardiac Surgery, National Institute of Cardiovascular Disease, Sher-E-Bangla Nagar, Dhaka, Bangladesh for CABG Surgery have been taken as study population.Sample Group:

Considering inclusion and exclusion criteria 80 patients were selected. This study population was divided into 2 groups 40 patients in each group.

Of them 40 patients was selected for MIDCAB surgery and 40 patients was selected for CCABG. Patients for MIDCAB surgery was enrolled as group A and CCABG as group B.

Sampling method:

Purposive sampling method

Sample selection:Inclusion criteria All elective CABG patients.Exclusion criteria Patients, who refused to be included in the study. Myocardial infarction within the last 3 months. Ejection fraction <30%. Emergency or redo CABG. Diffusely diseased with calcified artery.

Associated valve disease. Associated congenital cardiac disease. Associated hepatic, renal & pulmonary dysfunction. Patients undergoing OPCAB surgery Ethical issue:Prior to the commencement of this study, the research protocol was approved by the thesis committee (Local Ethical committee). The aims and objectives of the study along with its procedure, alternative treatment methods, risks and benefits of this study explained to the patients in easily understandable local language. Then informed written consent was taken from each patient. It was assured that all information and records would be kept confidential.

Methodology:After MIDCAB coronary artery bypass Surgery all patients monitored in the ICU and pulmonary function assessed. Preoperatively Lung function parameters, Vital Capacity (VC) and forced expiratory Volume in 1st sec (FEV1) were evaluated using a transportable spirometer unit. Each test was performed three times and the best results were selected For analysis, tests were then repeated on postoperative day (POD) 1 (6 hours after extubation), 3 and 5. Arterial blood gas analysis (PO2 and PCO2) were determined when breathing room air preoperatively and on POD 1, 3 and 5. Adequate analgesia was ensured. No central depressant or muscle relaxant was given.

Surgical Procedure: Patients were positioned with the left side elevated to more than 60 degrees. Saphenous vein graft was harvested from the right lower extremity.A 5 to 6 inch long incision was made over the fourth or fifth intercostals space depending on the angiographic anatomy.The incision was made 1 inch below and 1 inch medial to the left nipple and extended laterally to the mid to posterior axillaries to vertebral line. Pericardiotomy was done parallel and anterior to the phrenic nerve and extends from the apex of heart to the ascending aorta. Patient was heparin zed.Left lung was retracted downward and anteriorly to expose the descending thoracic aorta for proximal anastomosis of saphenous vein.LITA was anastomosed to the LAD.Deep pericardial sling and mechanical device Urchin were used to position the heart for optimal visualization of the lateral, posterior, inferior and the distal right coronary arteries. To maintain hemodynamic stability, some time patients were placed in trendelenburg position for grafting PDA, and OM.

The proximal anastomoses were done on the descending thoracic aorta or subclavian artery. After completion of anastomoses protamine was administerd for heparin reversal. After placing temporary pacing wire in the right ventricular epicardium, the pericardium and mediastinal fat was loosely approximated to cover the grafts and to prevent cardiac herniation. Chest wound was closed keeping two drain tube in situ.

PATIENT PROFILE

DEMOGRAPHICAge (In years) (Age & Sex have been collected & recorded in data sheet)Sex. (Male/Female)

CLINICALRisk factor like; HTN, COPD, DM, Asthma, Previous MI, Angina, Previous cerebrovascular diseases have been collected & recorded in data sheet)

HISTORY Systemic hypertension.(present/absent).

COPD or Asthma. .(present/absent).Smoker (Yes/No).Angina (present/absent; CCS Class I II III IV).DM. (present/absent).

Previous MI. (present/absent). Previous cerebrovascular diseases (present/absent).

A. EXAMINATION Hepatomegally (present/absent). Dependant Oedema (present/absent). Basal Creps (present/absent).

INVESTIGATIONSpirometry:FVC (Forced Vital Capacity) FEV1 (Forced Expiratory Volume in 1 sec) FEV1/FVC%

PEFR (Peck expiratory flow rate)TV (Tidal volume)

LABORATORY Arterial blood gas:

pH Po2 (Partial Pressure of Oxygen)

Pco2 (Partial Pressure of Carbondioxide)

DAao2 (Arterio-Alveolar Oxygen Difference)

MEASURES OF VARIABLES:

Pre-operative:-1) Coronary angiogram- done in all patients and findings recorded.2) Lung function test-Spirometric variables- FEV1 & FVC were

recorded. 3) Arterial blood gas variable (PaO2 PaCO2 AaDO2) before

anesthetic induction. Per-operative:- 1) Total operation time in minute.

2) Aortic cross-clamp (ACC) time in minute. 3) Extra corporeal circulation (ECC) Time in inute.

4) Number of grafts. 5) ABG-PH PO2 PCO2.

Post-operative:-1) Respiratory Rate2) ICU stay in days (Mean +SD)3) Mechanical ventilation time in hours (Mean +SD)4) Arterial blood gases (Po2, Pco2 PH

SPO2 ).5) Spirometric variables (FVC, FEV1,FEV/FVC%) on 1st 3rd & 5th

Post Operative day.Follow-up; All the patients have been followed up at 1st, 2nd and 3rd month postoperatively. Any pulmonary complication recorded.

DATA COLLECTION AND ANALYSIS:Data collected in a pre-designed form.All data analyzed by using computer based SPSS program.RESULTSOut 80 patients of CABG, 40 were in MIDCAB and the rest 40 were in On-pump conventional CABG. The findings derived from data analysis are furnished below.

5.1 Age distribution:Table I: Age distribution between groups Age (yrs) Group p value

MIDCAB (n=40) CCABG(n=40)

n % n %<40 7 17.5 5 12.540-50 5 12.5 5 12.550-60 10 25.0 10 25.0

≥60 18 45.0 20 50.0Mean ±SD 60.2 ± 14.0 55.5 ± 11.1 0.102NS

Range (30-78) (31-68.9)

NS= not significant P value reached from unpaired t- test

Table I shows that nearly half (45.0%) of the cases of MIDCAB group were >60 years age or above compared to 50.5% of the CCABG. The age category 50-60 years formed the second majority 25.0% in MIDCAB group and 25.0% in CCABG group). Very few cases were found between 40-50 years of age (12.5% in each group) and below 40 years of age (17.5% in MIDCAB and 12.5% in on-pump). The mean ages of MIDCAB and CCABG groups were 60.2 and 55.5 years respectively. The mean difference of age was statistically not significant (p>0.05) in unpaired-t test.

5.2 Distribution of patients between groups Table II: Sex distribution between groups Sex Group p value

MIDCAB (n=40)

CCABG(n=40)

n % n %Male 35 75.0 37 87.5 0.355 NS

Female 5 25.0 3 12.5

NS = Not significant (p>0.05)P value reached from Fisher’s exact test,

Table II compares the sex distribution between groups. A male predominance was observed in both the groups with 75.0% male in MIDCAB group and 87.5% male in CCABG group. The groups were statistically homogeneous relative to sex (p=0.355).

5.3 Distribution of preoperative NYHA functional class:Table III: Distribution of preoperative NYHA functional classNYHA Group p value

MIDCAB (n=40) CCABG (n=40)n % n %

Class I 5 12.5 0 0.00.046SClass II 21 52.5 28 70.0

Class III 14 35.0 12 30.0

S= significant

P value reached from Chi square test

Table III shows demonstrates the distribution of patients by NYHA functional class. Approximately 52.5% of the MIDCAB group belonged to NYHA Class-II, followed by 35.0% NYHA Class-III and 12.5% NYHA Class-I. In CCABG group 70.0% were classified as NYHA Class-II, 30.0% as NYHA Class-III and none belonged to Class-I. The mean difference of NYHA was statistically significant (p<0.05) in Chi square test. 5.4 Comparison of Risk Factors Table IV: Comparison of Risk FactorsRisk factors Group p value

MIDCAB (n=40) CCABG (n=40)n % n %

SmokingYes 12 30.0 12 30.0 1.000NS

No 28 70.0 28 70.0HTN

Yes 17 42.5 20 50.0 0.501 NS

No 23 57.5 20 50.0DM

Yes 9 22.5 7 17.5 0.576 NS

No 31 77.5 33 82.5Dyslipidemia

Yes 6 15.0 12 30.0 0.108 NS

No 34 85.0 28 70.0Family history of IHD

Yes 10 25.0 10 25.0 1.000 NS

No 30 75.0 30 75.0Old MI

Yes 21 52.5 18 45.0 0.502 NS

No 19 47.5 22 55.0

NS= not significant P value reached from Chi square test Table IV shows compares the distribution of risk factors between groups. In the MIDCAB group 52.5% of the patients had old MI, 42.5% HTN, 30% smoking, 22.5% DM, 15.0% dyslipidemia, and 25.0% family history, of ischemic heart disease. In CCABG group 50.0% HTN, 45.0% Old MI, 30.0% smoking, another 30.0% dyslipidemia, 17.5% DM, 25.0% family history. The mean difference of risk factor was statistically insignificant (p>0.05) in Chi square test.

5.5 Extent of disease by coronary angiogram:Table V: Comparison of extent of disease between groups.

Extent of disease Group p valueMIDCAB (n=40)

CCABG(n=40)

n % n %SVD 4 10.0 4 10.0

0.351NSDVD 18 45.0 11 27.5TVD 12 30.0 19 47.5LM 6 15.0 6 15.0

NS= not significant P value reached from Chi square test Analysis of distribution of extent of disease between groups demonstrates that 18(45%) of MIDCAB and 19(47.5%) CCABG had DVDs and TVDs respectively. The MIDCAB have 4 (10.0%) SVDs, while 6(15.0%) cases of LM diseases in each group.

5.6 Comparison of significant stenosis in different coronary arteries. Table VI: Comparison of significant stenosis in different coronary arteries. Significant stenosis (≥50% stenosis)

GroupMIDCAB CCABG

LM 75% 75%LAD 100% 97.4%DI 100% 87.5%LCX 95% 100%OMI 100% 87.5%OM2 100% 100%RI 100% 87.5%RCA 95% 95.5%PDA 100% 0%

Table VI compares the proportion of patients with percentage in different coronary arteries between the groups was significant stenosis (≥50 groups. The distribution as seen form the table is almost uniform with respect to all the coronary arteries except PDA, Where all the patients with PDA lesions were in MIDCAB group.

5.7 Distribution of grafts

Table VII: Distribution of graftsGroup p valueMIDCAB (n=40) CCABG (n=40)n % n %

1 graft 4 10.0 4 10.0

0.351 NS2 grafts 18 45.0 11 27.53 grafts 12 30.0 19 47.54 grafts 6 15.0 6 15.0NS= not significantP value reached from chi square test

Table shows displays the distribution of number of grafts between groups. 45% of the MIDCAB group required 2 grafts, 30% 3 grafts, 15.0% 4 grafts and another 10% 1 grafts. In CCABG group 47 .50% needed 3 grafts and 27.5% 2 grafts. 1 grafts and 4 grafts was 10.0% & 15% respectively.

5.8 Distribution of individual grafts

Table VIII: Distribution of individual graftsGroup p valueMIDCAB (n=40) CCABG (n=40)

n % n %LAD 40 100 40 100 -D1 5 12.5 7 15 0.745 NS

LCX 1 2.5 1 2.5 -OM1 4 12.5 11 30 0.055 NS

OM2 11 30 8 22.5 0.445 NS

R1 2 5 1 2.5 0.556 NS

RCA 12 32.5 13 35 0.813 NS

PDA 6 15 9 20 0.556 NS

NS= not significantP value reached from chi square test

Table shows displays the distribution of number of individual grafts between groups. Revascularization of LAD was done in 40 patients each in MIDCAB and CCABG group, followed by RCA 12 and 13, then OM2 11 and 8, OMI 4 and 11, PDA 6 and 9, D1 5 and 7, RI 2 and 1, and finally LCX each 1 respectively.

5.9 Preoperative lung function by spirometry:Table IX: Comparison of preoperative Lung Function Test (n=80).

Preoperative Lung Function Test

Group pvalue

MIDCAB (n=40)

CCABG(n=40)

FVC (L) 2.68 ±0.55 2.93 ±0.74 0.083NS

FEV1 (L) 2.20 ±0.53 2.45 ±0.65 0.071 NS

FEV1/FVC 0.82 ±0.10 0.85 ±0.18 0.328 NS

NS= not significant P value reached from unpaired t-test

Among the 3 variables for evaluation of preoperative lung function test like FVC, FEV1 and FEV1-FVC ratio, none was found to be significantly different between groups (2.68±0.55 vs. 2.93±0.74, p= 0.083; 2.20±0.53 vs 2.45±0.65, p=0.071 and 0.82 ±0.10 vs 0.85±0.18, p=0.328 respectively).

5.10 Comparison of preoperative arterial blood gas (ABG) analysis (just before doing surgery at OT).

Table X: Comparison of preoperative arterial blood gas (ABG) analysis (just before doing surgery at OT).Preoperative ABG variables

Group p value

MIDCAB CCABG

(n=40) (n=40)PaO2 134.43 ±5.84 132.87 ±12.77 0.544NS

D (A-a) O2 (torr) 53.90 ±7.42 51.0 ±9.49 0.192 NS

PaCO2 (torr) 40.23 ±2.62 40.03 ±1.71 0.728 NS

pH 7.42 ±0.02 7.43 ±0.02 0.124 NS

NS= not significant P value reached from unpaired t-test

Table X compares the preoperative arterial blood gas (ABG) analysis between MIDCAB and CCABG group. All the ABG variables, such as, PaO2, D (A-a) O2 (torr), PaCO2 (torr), pH were almost alike between groups (p>0.05).

5.11 Ventilation time and ICU stay:

Table XI: Comparison of ventilation time and ICU stay between groups

Ventilation time Group p valueand ICU stay MIDCAB

(n=40)CCABG(n=40)

Ventilation time (hours) 5.5 ±2.8 14.8 ±3.7 <0.001S

ICU stay (hours) 24.8 ±3.70 47.77 ±2.50 <0.001 S

S= significant P value reached from unpaired t-test

Table XI compares the ventilation time and ICU stay between and MID CAB and CCABG surgery. The ventilation time was observed to be significantly less in MID CAB than that required in CCABG (5.5±2.8 vs. 14.8±3.7 hours, p<0.001). The ICU stay period however, was also found to be significantly less in MIDCAB.

5.12 Postoperative arterial blood gas (AGB) analysis:

Table XII: Comparison of postoperative ABG analysis Postoperative ABG variables

Group p value

MID CAB (n=40)

CCABG(n=40)

ICU PaO2(torr) 296.5 ±32.4 234.8 ±10.7 <0.001S

3rd POD PaO2(torr) - - 77.3 ±2.1ICU D (A-a) O2 (torr) 378.5 ±27.3 439.2 ±10.3 <0.001S

3rd POD D (A-a) O2 (torr) - - 62.4 ±5.1

ICU PaCO2 (torr) 38.5 ±3.8 40.1 ±1.8 0.045S

3rd POD PaCO2 (torr) - - 43.6 ±2.2ICU pH 7.36 ±0.55 7.46 ±0.03 0.312NS

3rd POD pH - - 7.41 ±0.02

S= significant, NS= Not significant P value reached from unpaired t-test

Table XII demonstrates that postoperative ICU partial pressure of oxygen and ICU alveolar-arterial oxygen difference were significantly higher in MIDCAB group compared to those CCABG group (296.32.4 vs. 234.8±10.7 torr, p<0.001 and 378.5±27.3 vs. 439.2±10.3 torr, p<0.001 respectively). On the other hand ICU partial pressure of carbon dioxide was observed to be significantly less in the former group than that in the latter group (38.5±3.8 vs. 40.1±1.8 torr, p=0.045). Blood was taken half hour after extubation. The groups were not found to be different with respect to other ABG variables.

5.13 Postoperative lung function (by spirometry) test

Table XIII: Comparison of postoperative lung function test

Post operative lung function parameter

MIDCAB (n=40) CCABG(n=40)

P Value

Mean ±SD Mean ±SD

FVC by spirometryPOD1 2.30 ±0.50 2.49 ±0.60 0.135 NS

POD3 2.25 ±0.44 2.41 ±0.42 0.083 NS

POD5 2.22 ±0.49 2.43 ±0.52 0.071 NS

After 1st month 2.31 ±0.70 2.52 ±0.59 0.162 NS

After 2nd month 2.23 ±0.46 2.43 ±0.44 0.058 NS

After 3rd month 2.25 ±0.50 2.45 ±0.54 0.083 NS

FEVI by spirometryPOD1 1.81 ±0.46 2.04 ±0.47 0.055 NS

POD3 1.85 ±0.48 2.06 ±0.49 0.058 NS

POD5 1.88 ±0.49 2.07 ±0.50 0.083 NS

After 1st month 1.83 ±0.47 2.02 ±0.45 0.071 NS

After 2nd month 1.86 ±0.42 2.00 ±0.51 0.186 NS

After 3rd month 1.89 ±0.43 2.09 ±0.53 0.058 NS

FEVI/FVC by spirometryPOD1 0.80 ±0.11 0.84 ±0.14 0.249 NS

POD3 0.82 ±0.12 0.85 ±0.15 0.955 NS

POD5 0.81 ±0.10 0.83 ±0.16 0.966 NS

After 1st month 0.83 ±0.13 0.85 ±0.11 0.472 NS

After 2nd month 0.84 ±0.14 0.86 ±0.15 0.519 NS

After 3rd month 0.83 ±0.15 0.84 ±0.16 0.770 NS

NS= not significant P value reached from unpaired t-test

Postoperative outcome measured in terms of lung function test showed that, none of the variables of lung function test was any different between groups (Table XIII).

5.14. Pulmonary complication within 3 months:

Table XIV: Comparison of Mortality and Pulmonary Complication within 3 months.

Variables GroupMIDCAB (n=40)

CCABG(n=40)

n % n %Death within 3 months 0 0.0 1 2.5Pleural effusion 1 2.5 1 2.5

Table XIV demonstrates that there was no difference in pulmonary complication between two groups except single mortality in CCABG.

DISCUSSIONThe National Institute of Cardiovascular Diseases (NICVD), Dhaka is performing a pivotal role in the field of cardiovascular surgery in Bangladesh. NICVD is the only government institute, which is serving the nation in this aspect since her establishment in 1981.

This study was carried out in NICVD to evaluate the pulmonary functions after MIDCAB surgery, a routinely performed surgery in this institute.

This is a nonrandomized prospective clinical study done in National Institute of Cardiovascular Diseases (NICVD), Dhaka, during the period of July 2006 to June 2008. Sample size was 80 and sample was purposely determined. Data were collected by an interview schedule and chick list. Data were entered into a computer and data file was constructed. Data were analyzed by SPSS programme and tested by student's T-test and chi-square test.

The patients were divided in 2 groups – Group A: MIDCAB and Group B: C CABG.

The age distribution of the patients ranged from 30-78 years in MIDCAB group and 31-68.9 years in CCABG group with mean age 60.2 and 55.5 years respectively. Vargas et al. (1999) found the mean age to be 58 years while Westerdahl et al. (2003) found higher age (66 years) of the patients undergoing CABG. Lichtenberq et al. (2000) have showed that the mean of MIDCAB is 65.2 years. Our study also shows near about similar age distribution.

A male predominance was observed in both groups with 75.0% male in MIDCAB group and 87.5% male in CCABG group. P value was not significant between the groups.

Regarding NYHA functional class, approximately 52.5% of the MIDCAB group belonged to NYHA Class-II, followed by 35% NYHA Class-III and 12.5% NYHA Class-I. In CCABG group, about 70% were classified as NYHA Class- 11, 30% as NYHA Class-III and none belong to class-I. So, majority of the patients of both groups belonged to NYHA class II & III, which closely resembles the findings of Westerdahl et al. (2003).

Regarding the incidence of risk factors, both the groups were also comparable to each other. In the MIDCAB, 52.5% of the patients had old MI, 42.5% hypertension, 30% smoking, 22.5% DM, 15% dyslipidemia and 25% had family history of ischemic heart disease. In CCABG group, 50% hypertension, 45% old MI, 30% smoking, another 30% dyslipidemia, 17.5% DM and 25% family history of IHD. The study of Vargas (1999) revealed smoking and hypertension were the more prevalent risk factors like our study.

Analysis of distribution of extent of disease between the groups demonstrates that 18(45%) of MIDCAB and 19(47.5%) CCABG had more extent of diseases in DVD and TVD (triple vessel disease) respectively. Followed by TVDs 12(30%) and 11 (27.5%) in MIDCAB and CCABG respectively.

Regarding distribution of number of grafts between two groups, 45% of MIDCAB group required 2 grafts, 30% 3 grafts, 15% 4 grafts and another 10% 1 graft. In CCABG group, 47.5% needed 3 grafts and 27.5% 2 grafts.

Preoperative spirometry revealed that FVC and FEVI were not significant in MIDCAB group compared to their CCABG counterpart. Study done by Gerald et al. (2005) supports this result.

Ventilation time and ICU stay between MIDCAB and CCABG CABG surgery were recorded. The ventilation time was observed to be

significantly less in MIDCAB than that required in CCABG (5.5 ± 2.8 vs. 14.8 ± 3.7 hours). The ICU stay, however, was also found to be significantly different between groups. This finding closely resembles the findings of Gerald et al. (2005). But, finding of significance of ventilation time in off-pump group is also supported by the study of Gary et al. 2000.

Arterial blood gas (ABG) was analyzed preoperatively, at ICU and on 3rd postoperative day. Preoperative values were found not significant in MIDCAB vs. CCABG groups. Values recorded at ICU reveal that Pa02 and D(A-a)O2 were significantly better in MIDCAB group compared to those CCABG group (296.5 ± 32.4vs. 234.8 ± 10.7 torr, p < 0.001 and 378.5 ± 27.3 vs. 439.2 ± 10.3 ) torr, p < 0.001 respectively. On the other hand, ICU PaCO2 was observed to be significantly less in the former group than that in the latter group (38.5 ± 3.8 vs. 40.1 ± 1.8 torr, p = 0.045). The groups were not found to be different with respect to other ABG variables. These findings resemble with studies of Gerald et al. (2005) and Gary et al. (2000).

CCABG group had poorer gas exchange immediate postoperatively, and their extubation was delayed by ABG-based protocol even though they had no signs of pulmonary edema and a smaller decrease in compliance.

Tschernko et al. (2002) demonstrated that immediate postoperative oxygenation and shunt fractions were better in the MIDCAB group. Gerald WS et al (2005) also echoed having similar findings. Cimen et al. (2003) found no significant differences between MIDCAB and on-pump groups in gas exchange, spirometry and time of extubation.

Patients were followed up 3 month after operation. Follow up examination included physical examination, any pulmonary, complication, and Spirometry. Postoperative outcome measured in terms of lung function test showed that, none of the variables of lung function test were different between groups. These findings are supported by study of Gerald et al. (2005).

Regarding pulmonary complication, 1 patient from each group had pleural effusion and 1mortality in CCABG due to ARDS.

SUMMARYThe mean ages of MIDCAB and CCABG groups were 60.2 and 55.5 years respectively. The groups were statistically not significant in terms of age (p=0.102).

The groups were statistically homogeneous relative to sex (p=0.355).

Approximately 52.5% of the MIDCAB group belonged to NYHA Class-II, followed by 35.0% NYHA Class-III and 12.5% NYHA Class-I. In CCABG group 70.0% were classified as NYHA Class-II, 30.0% as NYHA Class-III and none belonged to Class-I. The groups were statistically significant .

Analysis of distribution of extent of disease between groups demonstrates that 18 (45%) of MIDCAB and 19 (47.5%) CCABG had DVDs and TVDs respectively. The MIDCAB have 4 SVDs, while 6 (15.0%) cases of LM diseases in each group.

Table VI compares the proportion of patients with significant stenosis in different coronary arteries between the groups which shows almost uniform distribution except PDA, where all the patients with PDA lesion were in MIDCAB group. In the MIDCAB group 52.5% of the patients had old MI, 42.5% HTN, 30% smoking, 22.5% DM, 15.0% dyslipidemia, and 25.0% family history, of ischemic heart disease. In CCABG group 50.0% HTN, 45.0% Old MI, 30.0% smoking, another 30.0% dyslipidemia, 17.5% DM, 25.0% family history of IHD found.Table XI compares the ventilation time and ICU stay between and MIDCAB and CCABG surgery. The ventilation time was observed to be significantly less in MIDCAB than that required in CCABG (5.5±2.8 vs. 14.8±3.7 hours, p<0.001). The ICU stay period however, was also found to be significantly less in MIDCAB.Table XIV demonstrates that there was no difference in pulmonary complication between two groups except single mortality in CCABG which was due to development of ARDS.

CONCLUSIONIt may be concluded that MIDCAB is a safe procedure that avoids the potential risks of CPB. It may also be concluded that MIDCAB group yielded better gas exchange, earlier extubation and early discharge from ICU management.

RECOMMENDATIONWe recommended MIDCAB should be considered better than CCABG for gas exchange, earlier extubation and less ICU stay time in aged patients.

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